The present invention relates to a pump control mechanism, a printer incorporating the same, and a pump control method.
In a majority of relatively low performance type printers, a cartridge for storing ink is mounted on a carriage. On the other hand, in some high performance type printers, the cartridge is not mounted on the carriage but on the housing of the printer. In printers of this type, even when the ink residual amount varies, a fluctuation can be suppressed in the weight of the carriage. Thus, the printers of this type achieve precise control of the motion of the carriage.
In the printers of the above-mentioned type, a liquid container is mounted on the carriage. Then, a cartridge is connected to the liquid container via a liquid pipe, so that ink can be supplied from the cartridge to the liquid container. Further, one end of an air pipe is connected to the cartridge. The other end of the air pipe is connected to a bellows pump in a pump unit. When the bellows pump is driven, air is supplied into the cartridge via the air pipe. Then, by this air pressure, the ink can be supplied from the cartridge to the liquid container via the liquid pipe.
An example of a printer using such air pressure is disclosed in Japanese Patent Publication No. 2002-510252A. Specifically, the printer comprises: a reciprocating member for performing reciprocating motion and thereby compressing air; a pump motor for causing the reciprocating member to perform the reciprocating motion; and an electric power supplying section for supplying electric power to the pump motor until the pressure of the liquid container reaches a predetermined pressure.
Meanwhile, when the bellows pump is driven by the pump motor, the noise generated from noise sources such as the pump motor and a conversion mechanism becomes problematic. In the operation sound generated from the printer, this kind of noise is remarkably loud. Thus, its reduction is an issue.
In particular, when the bellows pump is expanded and contracted, the external load acting on the pump motor varies according to a change in the internal pressure of the bellows pump, so that the revolution rate of the pump motor fluctuates depending on the change. Thus, the noise generated from the noise source also fluctuates according to the fluctuation of the revolution rate. Meanwhile, when the noise fluctuates according to the revolution rate, a problem arises that the noise is felt stronger to the ear in comparison with the case that sound at a constant level is generated stationary from a noise source. That is, when noise of the same level is generated, noise having a fluctuated magnitude is felt noisier than noise generated stationary.
This problem of noise arises at each time that the pump motor operates during the usage of the printer. Accordingly, a problem occurs wherein the problem of noise continues during the usage of the printer. Thus, it is desired to achieve quiet operation at least in a steady state that the initial operation of the printer has been completed. Here, in the control of the above-mentioned pump motor, in a case where a sensor such as a rotary encoder capable of detecting the revolution rate is installed so that the revolution rate of the pump motor is controlled using a feedback signal from the sensor, the noise can be reduced. Nevertheless, the installation of the rotary encoder or the like causes a problem such as a cost increase.
Nevertheless, even if the noise reduction were possible merely by the detection of the signals from the position sensor and the pressure sensor, in a case where a fault occurs in the position detection sensor or the pressure sensor, the problem of noise is not solved. That is, the occurrence of a fault in the position detection sensor or the pressure sensor causes a situation not merely that appropriate control of the revolution rate of the pump motor cannot be performed but also that the revolution rate increases in contrast to the intention. Further, the pump motor continues to revolve indefinitely, and thereby causes a problem that the problem of noise continues during the continuation of the revolution.